The SqlParameter is already contained by another SqlParameterCollection when NOT using a SqlParameterCollection

I have the following that is throwing a The SqlParameter is already contained by another SqlParameterCollection exception in the catch block.

What I find odd is that nowhere do we create a SqlParameterCollection. Each time we create a new instance so the SqlParameter is never used more than once. And another oddity is that test contains the correct results from the stored procedure and returns the results to the calling method, but when I step one more time from line 3 to 4 is when it decides to enter the catch block. Not at line 33 where I would expect it to occur... If it helps any we switched from an ObjectContext to a DbContext using the CodeFirst generation tools. All other database interactions and stored procedures used are working as expected.

1    try
2    {
3        tempMessages = Context.CheckExistingTables(importSession.ImportSessionID).ToList();
4    }
5    catch (Exception e)
6    {
7        this.LogError("Error validating the import file entities", e);
8        tempMessages.Add(new ErrorMessage() { ErrorType = 3, Message = string.Format("Error validating the import file entities: {0}", e.Message) });
9    }
...
20    public IEnumerable<ErrorMessage> CheckExistingTables(Guid? importSessionID)
21    {
22        SqlParameter importSessionIDParameter;
23
24        if (importSessionID.HasValue)
25        {
26            importSessionIDParameter = new SqlParameter("importSessionID", importSessionID);
27        }
28        else
29        {
30            importSessionIDParameter = new SqlParameter("importSessionID", typeof(System.Guid));
31        }
32
33        var test = Database.SqlQuery<ErrorMessage>("Import.CheckExistingTables @importSessionID", importSessionIDParameter);
34        return test;
35    }